The present invention generally relates to flame and spark detection, and is usable in a variety of fields including for instance fire alarming and flame monitoring of e.g. oil pipe flames and rocket launches, but also to detect electrical coronas, discharges, and to detect lightening at day time as a fast warning, or for triggering fast switch-off of equipment.
Many simple automatic fire alarms of today are based on a smoke detector. However, in some situations a smoke detector alone does not give reliable information about fire related accidents. Thus, more sophisticated and reliable devices are under continuous development.
A common approach is to simultaneously use two or more detectors of different nature, for example a smoke detector and an infrared detector. However, even such a detector combination may sometimes give false information. In attempts to overcome such limitation there was invented an infrared detection device measuring not only infrared emission from the fire, but also a frequency of flame oscillations. This gives a clear signature of a fire and also improves the signal-to-noise ratio. There have also been attempts to combine IR and UV sensitive detectors. However, the UV detectors used are very expensive and of low sensitivity.
Nevertheless, there are a few drawbacks of such approaches. Firstly, such technique is complex and thus costly, the infrared detector needs for instance cooling. Furthermore, the power consumption of such an approach is rather high.
Infrared detectors as such have typically not very good signal-to-noise or signal-to-background ratios. Thus, there is a need of another detecting principle, which is simple and reliable.
Accordingly, it is an object of the present invention to provide a flame detector, which provides for high signal-to-noise and signal-to-background ratios to thereby obtain a reliable detection.
A further object of the invention is to provide such a flame detector, which provides for high sensitivity.
Still a further object of the invention is to provide such a flame detector, which provides for low power consumption.
Yet a further object of the present invention is to provide such a flame detector, which is effective, fast, accurate, reliable, and of low cost.
These objects among others are, according to the present invention, attained by flame detectors, automatic fire alarms, and methods related thereto as claimed in the appended claims.
By the provision of a gaseous-based detector provided with a photocathode as claimed in the appended claims for detection of flames and discharges a simple and cheap detector is obtained, which is also reliable and exhibits excellent detecting characteristics.
Further, the detector is insensible to visible light, has high output signals for simple signal processing, and it can be manufactured in large size, i.e. with large sensitive area (square meters) of extremely high sensitivity.
Further characteristics of the invention and advantages thereof will be evident from the detailed description of preferred embodiments of the present invention given hereinafter and the accompanying FIGS. 1-4, which are given by way of illustration only, and thus are not limitative of the present invention.